JPS5919362B2 - Variable sample period controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sample period control device, and more particularly to a variable sample period control device that varies the sample period in response to changes in dead time in a process system.

Component control plays a very important role in control systems for improving product quality, uniformity, pollution prevention, energy conservation, etc. This component control generally requires a large amount of wasted time.
Furthermore, the dead time changes depending on the quantity to be controlled, such as the magnitude of the fluid flow rate, making control extremely difficult. For this reason, sample values have conventionally been introduced to remove the influence of this wasted time. However, with conventional sample value control devices, even if you change the manipulated variable and try to execute control after the effect is completely reflected in the process variable, sample value control is performed at a fixed cycle, so the flow rate in the process system changes. However, if the wasted time changed as a result, good control could not be achieved.

An object of the present invention is to provide a sample control device that can perform good control even when the waste time of a process system varies depending on the quantity to be controlled.

To achieve this objective, when updating the control output intermittently based on sample values at certain time intervals, the sample period Ts is set to a value obtained by continuously detecting the changing flow rate of the process system. Based on Ts
The sample value is controlled at an interval of Calculate the wasted time using the above formula at the interval, and perform sample control operation after the time has elapsed by adding the time multiplied by the time constant, even in a system where the wasted time changes depending on the flow rate. Enable good sample value control.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, fluid A to be controlled is guided through piping 11,
After detecting the flow rate with the flow rate transmitter 12, the mixing reaction tank 1
Put it in 3.

On the other hand, with respect to this fluid A, fluid B is introduced through piping 14, the flow rate is measured by a flow rate oscillator 15, and the fluid B is introduced into a mixing reaction tank 13 through a control valve 16 to mix and react with fluid A to obtain fluid CIT. , the fluid C is transferred to the next process via piping 18. The control system gives a signal obtained by multiplying the flow rate signal of fluid A from the flow rate transmitter 12 by a ratio α to a multiplier 20, and the multiplier 20
The output of is set as the setting value of the flow rate controller 21, and the output of the flow rate transmitter 15 is
The flow rate controller 21 performs a comparison adjustment calculation with the flow rate signal of fluid B, outputs the result to the control valve 16, and outputs the result to the control valve 16.
operate.

Further, a signal obtained by measuring the components of the fluid C by a component transmitter 22 is supplied to a component controller 23 using a sampling control method. The component adjuster 23 compares and adjusts the component setting value with the output of the component transmitter, inputs the adjusted output into the multiplier 20, and corrects and controls the mixing ratio of fluid A and fluid B. In other words, fluid B is injected by multiplying the flow rate of fluid A by a fixed ratio α, and the injection ratio of fluid B to fluid A is corrected by the component of fluid C created by mixing and reacting fluid A and fluid B. . In the component controller 23 of the sampling control type, the sample period is set to Fhl[ by the variable sample period calculator 24, and changes based on the flow rate value of the fluid A. Note that the variable sample period calculator calculates the waste time TD associated with fluid transfer, which has a large effect on the sample period Ts, using the flow rate detector 12.
This is determined based on the detected flow rate of fluid A.

The first method is to continuously integrate the supplied fluid flow rate from a certain point, hold this integrated value and the integrated time up to that point, and then calculate the integrated value from a control point that has been measured in advance. The cumulative time when the volume of piping, tanks, etc. up to the process variable detection point becomes equal to the volume VO is specified as wasted time. This relationship is expressed as follows. Also, the second
The method is to intermittently sample the supplied fluid flow rate a predetermined number of times, hold the number of samples n and the back-calculated value of the sampled flow rate, integrate the back-calculated values, and divide this total value by the number of samples n. The time obtained by multiplying the volume value VO measured in advance is the wasted time T.

It is specified as This relationship is expressed as follows. The waste time T identified in this way. The sampling period T8 is determined based on the following equation and is expressed from the relationship with the time constant T and constant K of the process system. This sampling period Ts is a dead time T due to a change in fluid flow rate.

A sample pulse signal corresponding to the period T8 is output to the component controller 23. Next, the operation of the apparatus constructed as described above will be explained with reference to FIG.

If the flow rate of fluid A is constant, the waste time is constant,
Therefore, the period of the sample pulse calculated by the variable sample period calculator 24 also becomes a constant value, and the component controller 2
3 performs sample control periodically.

By the way, in general, when the flow rate changes, the wasted time also changes, and may change from about several minutes to several tens of minutes.

The flow rate of the fluid A is detected by the flow rate transmitter 12, and based on this detection signal, the variable sample period calculator 24 calculates the waste time T.
. is calculated, and the time obtained by adding a time several times the time constant is compared with the elapsed time of the previous sample value control. When the elapsed time of the previous sample value control is equal or the latter is greater, the sample value control command is sent to the component controller 23. and execute control operations. Such operations are repeated thereafter to perform sample value control. As described above, according to the present invention, sample value control of a process system in which dead time fluctuates with changes in the physical quantity to be controlled can be achieved.

Although the present invention has been described in terms of an embodiment of the present invention, it is not limited thereto, and it goes without saying that it can also be carried out in software.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention in a block configuration, and FIG. 2 is a diagram showing the relationship between manipulated variables and process variables. 11...Piping, 12...Flow rate transmitter,
13...Mixing reaction tank, 14...Piping, 15...Flow rate transmitter, 16...Control valve, 17...Fluid C , 18... Piping, 19... Ratio device, 20... Multiplier,
21...Flow rate controller, 22...Component transmitter, 23...Component controller, 24...
Variable sample period calculator.

Claims (1)

[Claims] 1. In an apparatus for sampling control of a process system in which dead time varies according to changes in process flow rate, there is provided a means for detecting a process flow rate, and a means for integrating the flow rate detected by the means from a certain point in time. A means for outputting an integrated time and an integrated value, and a method that indicates that when the integrated value of this means becomes equal to the volume value of piping, tanks, etc. from a preset control point to a process variable detection point, the integration time for that integrated value is wasted. A waste time calculation means that is held as time, and a means that calculates a value obtained by adding the waste time held by this means and a value obtained by multiplying the time constant of the process system by a coefficient as a sampling period in sampling control. A variable sample period control device characterized by: 2. In a device that performs sampling control on a process system in which dead time varies according to changes in process flow rate, there is a means for detecting the process flow rate, and the flow rate detected by this means is intermittently sampled, and the number of samples and the sample flow rate are recorded. A means for outputting the back-calculated value, and a means for integrating the back-calculated value of the sample flow rate of this means and dividing this total value by the number of samples. A waste time calculating means that holds the time obtained by multiplying the volume value of , as a waste time, and a value obtained by adding the waste time held by this means and the value obtained by multiplying the time constant of the process system by a coefficient in sampling control. A variable sampling period control device comprising: means for calculating a sampling period.